Addendum: A dispersive analysis of η ' → π + π - γ and η ' → ℓ + ℓ - γ

Abstract

In this addendum to Ref. [1] we show that the mismatch between the $\rho$ - $\omega$ mixing parameter ${ϵ}_{\rho \omega }$ as extracted from ${\eta }^{\text{'}}\to {\pi }^{+}{\pi }^{-}\gamma$ and $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}$ can be resolved by including higher orders in the expansion in $e^2$ in the description of the ${\eta }^{\text{'}}\to {\pi }^{+}{\pi }^{-}\gamma$ decay. We repeat the analysis in this extended framework and update the numerical results accordingly.